1. Field of the Invention
This invention relates generally to imaging systems. More specifically, the present invention is directed to systems and methods of image processing in which a pixel gradient as well as value comparison are used to improve image quality.
2. Background Discussion
Medical imaging techniques provide doctors and medical technicians with valuable data for patient diagnosis and care. Various imaging techniques include cardiac angiography, peripheral angiography, radiography, computed tomography and positron emission tomography. All of these imaging techniques produce medical images that are studied by medical personnel. A higher quality image leads to more accurate diagnosis.
Radiography is the use of certain spectra of electromagnetic radiation, usually x-rays, to image a human body. Angiography, a particular radiographic method, is the study of blood vessels using x-rays. An angiogram uses a radiopaque substance, or contrast medium, to make the blood vessels visible under x-ray. Angiography is used to detect abnormalities, including narrowing (stenosis) or blockages (occlusions), in the blood vessels throughout the circulatory system and in certain organs.
Cardiac angiography, also known as coronary angiography, is a type of angiographic procedure in which the contrast medium is injected into one of the arteries of the heart, in order to view blood flow through the heart, and to detect obstruction in the coronary arteries, which can lead to a heart attack.
Peripheral angiography, in contrast, is an examination of the peripheral arteries in the body; that is, arteries other than the coronary arteries. The peripheral arteries typically supply blood to the brain, the kidneys, and the legs. Peripheral angiograms are most often performed in order to examine the arteries which supply blood to the head and neck, or the abdomen and legs.
Computed Tomography (CT), originally known as computed axial tomography (CAT or CT scan), is an imaging technique that uses digital geometry processing to generate a three dimensional image of internal features of an object from a series of two-dimensional x-ray images taken around a single axis of rotation. An iodine dye, or other contrast material, may be used to make structures and organs easier to see on the CT picture. The dye may be used to check blood flow, find tumors, and examine other problems.
Positron emission tomography (PET) imaging may also be used. In PET imaging, a short-lived radioactive tracer isotope, which decays by emitting a positron, and which has been chemically incorporated into a metabolically active molecule, is injected into the patient. The radioactive decay of the positrons is measured to generate an image.
When imaging techniques produce images, the images have a dataset of pixels or voxels (described in more detail below) that can be modified to increase the image quality. For example, medical volumetric dataset sizes have been expanding rapidly with the new advanced CT scanners. For example, typical CT machines from Siemens® Medical Solutions can generate a pixel image dataset at a size of 512×512×4096. The capacity to visualize such datasets with high interactivity and high image quality is helpful to medical professionals in diagnosing disease.
Ray-casting is one technique to generate images. However, interactivity is difficult to achieve due to intensive computation and cache-unfriendly memory access. The large number of sampling rays, which grow as a function of O(n2) (where n is image resolution), makes the technique even less efficient.
In order to increase the speed of the technique to render an image, usually a different rendering scheme is used for images during interaction (interactive mode) and then when a user stops and examines the image (definitive mode). Thus, the use of different methods has been one approach to improve the interactive mode performance. Other approaches include using nearest neighbor interpolation method as well as reducing rendered image resolution.
Unfortunately, most of the methods currently used compromise the image quality. For example, reducing the rendered image resolution (in Ray-Casting, it means shooting fewer number of rays) is achieved by rendering a smaller image (lower resolution) and then scale the image in 2D to the appropriate resolution.
However this approach is not optimal for balancing the rendering quality and performance because the rendering speed is unacceptably slow. Furthermore, reducing the image resolution by 4 or more in each dimension usually results in poor image quality.
Therefore, it would be an advancement in the state of the art to provide a system and method of generating high quality image data in an interactive mode with high frame rates.